I would suggest you look at the reproduction "Up-Start" or the "Sparky Start System" options.
These are mechanical devices that take place of the floor starter button. The "Up Start" is a lever that mounts to the steering column mount. You just pull up to start the car. Very easy installation and works very well. I have an original one in my car and it works very well.
I have not used the "Sparky Start System" that uses the spark control lever to start the car. If you push the spark lever all the way up, it will activate the starter.
Both of these designs have been around for many years, I think from the 1930's. No modifications to the electrical or any other part of the car. May be would be easier than installing an solenoid and push button. Brattons have them in their catalog, may be others also have them.
Just my opinion.
Chris W.